A broadband optical cavity spectrometer for measuring weak near-ultraviolet absorption spectra of gases

Abstract

Abstract. Accurate absorption spectra of gases in the nearultraviolet (300 to 400 nm) are essential in atmospheric observations and laboratory studies. This paper describes a novel incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) instrument for measuring very weak absorption spectra from 335 to 375 nm. The instrument performance was validated against the 3 B 1 -X 1 A 1 transition of SO 2 . The measured absorption varied linearly with SO 2 column density and the resulting spectrum agrees well with published spectra. Using the instrument, we report new absorption cross-sections of O 3 , acetone, 2-butanone, and 2-pentanone in this spectral region, where literature data diverge considerably. In the absorption minimum between the Huggins and Chappuis bands, our absorption spectra fall at the lower range of reported ozone absorption crosssections. The spectra of the ketones agree with prior spectra at moderate absorptions, but differ significantly at the limits of other instruments' sensitivity. The collision-induced absorption of the O 4 dimer at 360.5 nm was also measured and found to have a maximum cross-section of ca. 4.0 × 10 −46 cm 5 molecule −2 . We demonstrate the application of the instrument to quantifying low concentrations of the shortlived radical, BrO, in the presence of stronger absorptions from Br 2 and O 3 .

Absolute ozone absorption cross section in the Huggins Chappuis minimum (350–470 nm) at 296 K

“…Our measurements are consistent most with Brion et al (1998) with the exception of the minimum region from 375-390 nm, where our absorption cross section shows a lower minimum, but agrees within the combined uncertainty. Our measurements are also very consistent with those of Chen and Venables (2011), but their measurements do not extend past 375 nm. In addition, more defined O 3 structural features were observed in this work, Brion et al (1998), and Chen and Venables (2011) when compared to the other literature cross sections (Burrows et al, 1999a;Voigt et al, 2001;Bogumil et al, 2003).…”

“…Our measurements are also very consistent with those of Chen and Venables (2011), but their measurements do not extend past 375 nm. In addition, more defined O 3 structural features were observed in this work, Brion et al (1998), and Chen and Venables (2011) when compared to the other literature cross sections (Burrows et al, 1999a;Voigt et al, 2001;Bogumil et al, 2003). The measurements also agree within 0.5 % at 404 nm with Fuchs et al (2009), in which CRDS was used to measure the O 3 cross section, with the highest precision currently available within this wavelength range, to quantify its interference associated with measurements of NO 2 at the single wavelength of a diode laser.…”

“…Fig. 4 shows the O 3 absorption cross section measured at 295 K and 820 hPa, together with previously measured cross sections (Burkholder and Talukdar, 1994;Brion et al, 1998;Burrows et al, 1999a;Voigt et al, 2001;Bogumil et al, 2003;Fuchs et al, 2009;Chen and Venables, 2011) obtained from the Mainz Spectral Database (Keller-Rudek and Moortgat, 2011) and plotted for vacuum wavelengths. The Burkholder et al (1994), Fuchs et al (2009), and Chen and Venables (2011) spectra were corrected from air to vacuum wavelength using Eq.…”

“…Prior to the measurements in this work, the lowest reported O 3 cross section were those of Brion et al (1998) at 377.5 nm with a σ O 3 = 4.4×10 −24 cm 2 and a reported uncertainty of 4 % near the absorption minimum Chen and Venables (2011) examined the near-UV region from 335-375 nm, just to the short wavelength side of the minimum. These authors suggested that the absorption cross section in this region would be even lower than seen in previous studies (Brion et al, 1998;Burrows et al, 1999a;Voigt et al, 2001;Bogumil et al, 2003;Chen and Venables, 2011). In this work, the minimum was observed to be lower than the Brion et al (1998) value, at 385.6 nm with σ O 3 = 3.4×10 −24 cm 2 , although the two measurements are consistent within their combined uncertainty.…”

“…This technique was first described in the literature by Fiedler et al (2003), and has subsequently been used for spectroscopic measurements of NO 2 , NO 3 , CHOCHO, HONO, and other trace gasses (Venables et al, 2006;Langridge et al, 2006;Gherman et al, 2008;Langridge et al, 2008;Washenfelder et al, 2008;Thalman and Volkamer, 2010). More recently, Chen and Venables (2011) used an IB-BCEAS with an arc lamp to measure the O 3 cross section in the near-UV from 335-375 nm.…”